What is the possible root causes of the dendrite growth? How long its take to cause this dendrite growth? Can dendrite growth cause electrical short? Is there any particular location on PCBA that dendrite tend to grow?

The last time I encountered dendrite growth, it was within a component package. I believe we were experiencing it within a crystal. The root cause was water intrusion during in line wash. The component was supposed to have been sealed and safe for wash, however, destructive testing revealed that there was moisture intrusion. The combination of the moisture, heat, and whatever impurities got in there caused the dendrite growth. In our case, it was conductive, and caused failures.

Yes dendrites can cause electrical shorts. The first stage of dendritic growth is a dark fern like pattern which reduce surface insulation between anode and cathode. In a more advanced stage the ferns transfer the plating metals of the conductors and create dead shorts.

In a previous life I did a lot of experiments with growing dendrites and my findings were that you need 4 elements to be present to create them.

1) DC low voltage +/- 10V low current

2) Humidity

3) Exposed metal conductors

4) Surface to grow

If you eliminate one of those four you can�t get dendrites.

Most books talk about Ionics as a key component, but in my experiments Co2 in the air was enough to start the process (they grew as fast on a clean board as on a contaminated board).

Also in terms of time to create dead shorts pure tin was unbeatable, another thing to think about in this lead-free world.